Method of and apparatus for automatically controlling pressure in holding furnace incorporated in low pressure die-casting system
First Claim
1. A method of automatically controlling the pressure in a holding furnace incorporated in a low pressure die-casting system by controlling the pressurized gas to be supplied to the molten metal holding furnace using a proportional pressure control valve operated by a microcomputer, comprising the steps of:
- reading out a desired pressure Pi+1 at a time ti+1 which is a unit time ahead of a time ti from a desired pressurization pattern of the time--pressure curve associated with said holding furnace which has been stored in said microcomputer beforehand;
reading out an input command value Vo corresponding to said desired pressure Pi+1 from the steady values of the output pressure which are associated with the input command values of said proportional pressure control valve, said input command values being stored in said microcomputer beforehand;
detecting a pressure Pm in said holding furnace at said time ti ;
calculating a pressure deviation Δ
P from said desired pressure Pi+1 and said pressure Pm in said holding furnace;
calculating a correction value Vd by multiplying said pressure deviation Δ
P by a preset gain G;
calculating an input command value V by adding said correction value Vd to said input command value Vo; and
sending said input command value V to said proportional pressure control valve.
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Accused Products
Abstract
Disclosed is a method of and an apparatus for automatically controlling the pressure in a holding furnace incorporated in a low pressure die-casting system in accordance with a desired pattern. A proportional pressure control valve operated by a microcomputer is provided in a pressurized gas supply circuit for supplying pressurized gas into the holding furnace. The pressure in the holding furnace is changed in accordance with a pattern which is as close as possible to a desired pressurization pattern by sending to the proportional pressure control valve a command value obtained by adding to an input command value of the proportional pressure control valve a correction value calculated by a predetermined computing method.
11 Citations
7 Claims
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1. A method of automatically controlling the pressure in a holding furnace incorporated in a low pressure die-casting system by controlling the pressurized gas to be supplied to the molten metal holding furnace using a proportional pressure control valve operated by a microcomputer, comprising the steps of:
- reading out a desired pressure Pi+1 at a time ti+1 which is a unit time ahead of a time ti from a desired pressurization pattern of the time--pressure curve associated with said holding furnace which has been stored in said microcomputer beforehand;
reading out an input command value Vo corresponding to said desired pressure Pi+1 from the steady values of the output pressure which are associated with the input command values of said proportional pressure control valve, said input command values being stored in said microcomputer beforehand;
detecting a pressure Pm in said holding furnace at said time ti ;
calculating a pressure deviation Δ
P from said desired pressure Pi+1 and said pressure Pm in said holding furnace;
calculating a correction value Vd by multiplying said pressure deviation Δ
P by a preset gain G;
calculating an input command value V by adding said correction value Vd to said input command value Vo; and
sending said input command value V to said proportional pressure control valve. - View Dependent Claims (2, 3, 4)
- reading out a desired pressure Pi+1 at a time ti+1 which is a unit time ahead of a time ti from a desired pressurization pattern of the time--pressure curve associated with said holding furnace which has been stored in said microcomputer beforehand;
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5. An apparatus for automatically controlling the pressure in a holding furnace incorporated in a low pressure die-casting system, comprising:
- a pressurized gas source;
a pressure reducing valve;
a proportional pressure control valve and a surge tank which are connected in that order between said pressurized gas source and said holding furnace so as to introduce the gas from said pressurized gas source to the interior of said holding furnace;
a first pressure sensor for detecting the inside pressure (Pm) of said holding furnace;
a second pressure sensor for detecting the inside pressure (Ps) of said surge tank;
a microcomputer for controlling said proportional pressure control valve;
a first A/D converter for A/D-converting the output of said first pressure sensor and inputting the result to said microcomputer;
a second A/D converter for A/D converting the output of said second pressure sensor and inputting the result to said microcomputer;
a D/A converter for D/A converting the output of said microcomputer and sending the same to said proportional pressure control valve, wherein said microcomputer stores a desired pressurization pattern of the time--pressure curve associated with said holding furnace, as well as steady values of the output pressure which are associated with the input command values of said proportional pressure control valve, reads out a desired pressure Pi+1 at a time ti+1 which is a unit of time ahead of a time t1, reads out an input command value Vo of said proportional pressure control valve which corresponds to said desired pressure Pi+1, calculates a pressure deviation P from said desired pressure Pi+1 and said pressure Pm in said holding furnace which has been sent from said first pressure sensor, calculates a pressure deviation P, between the pressure Ps in said surge tank and the pressure Pm in said holding furnace, and sends to said proportional pressure control valve an input command value V which is obtained by adding to said input command value Vo a correction value Vd obtained by multiplying said pressure deviation P by a gain G set in accordance with said pressure deviation (P1).
- a pressurized gas source;
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6. An apparatus for automatically controlling the pressure in a holding furnace incorporated in a low pressure die-casting system, comprising:
- a pressurized gas source, a first supply including a pressure reducing valve and a proportional pressure control valve which are connected in that order between said pressurized gas source and said holding furnace so as to introduce the gas from said pressurized gas source to the interior of said holding furnace;
a second supply including a second pressure reducing valve, a solenoid valve and a flow rate control valve which are connected in that order between said pressurized gas source and said holding furnace for supplying gas to the interior of said holding furnace separately from said first supply;
a pressure sensor for detecting the inside pressure of said holding furnace;
a microcomputer for controlling said proportional pressure control valve and said solenoid valve;
an A/D converter for A/D-converting the output of said pressure sensor and inputting the same to said microcomputer;
a D/A converter for D/A converting the output of said microcomputer and sending the same to said proportional pressure control valve, wherein said microcomputer stores a desired pressurization pattern of the time--pressure curve associated with said holding furnace, as well as steady values of the output pressure which are associated with the input command values of said proportional pressure control valve, reads out a desired pressure Pi+1 at a time ti+1 which is a unit of time ahead of a time ti, reads out an input command value Vo of said proportional pressure control valve which corresponds to said desired pressure Pi+1, calculates a pressure deviation P from said desired pressure Pi+1 and said pressure Pm in said holding furnace which has been sent from said pressure sensor, and sends to said proportional pressure control valve an input command value V which is obtained by adding to said input command value Vo a correction value Vd obtained by multiplying said pressure deviation P by a present gain G; and
sends to said solenoid valve a signal for opening said solenoid valve at a time in said desired pressurization pattern which corresponds to an inflection point J+1 where the rate at which the pressure is raised increases with respect to time, and a signal for closing said solenoid valve before the time corresponding to an inflection point J+2 where the rate at which the pressure is raised decreases. - View Dependent Claims (7)
- a pressurized gas source, a first supply including a pressure reducing valve and a proportional pressure control valve which are connected in that order between said pressurized gas source and said holding furnace so as to introduce the gas from said pressurized gas source to the interior of said holding furnace;
Specification